Hydraulically loaded rolling mills

ABSTRACT

Hydraulically loaded rolling mills wherein the improvement comprises measuring means stretched over a distance between the measuring positions representing the roll gap of a rolling mill for measuring indirectly a change of the roll gup by detecting and signalling the tensile stress originated from elastic deformation of said measuring means.

United States Patent 1 Hirai et al.

HYDRAULICALLY LOADED ROLLING MILLS Inventors: Masuhiko Hirai; Toshiharu Takatsu; Kazuyoshi Hashimoto; Akira Hozoji, all of Hiroshima, Japan Assignee: Mitsubishi Jukogyo Kabushiki Kaisha, Tokyo, Japan Filed: Nov. 12, 1970 Appl. No.: 88,699

Foreign Application Priority Data Nov. 18, 1969 Japan ..44/91818 U.S. Cl ..72/8 Int. Cl. ..B21b 37/08 Field of Search ..72/8, 21, 245

n 1 3,709,007 1 Jan. 9, 1973 [56] 7 References Cited UNITED STATES PATENTS Primary Examiner-Richard J. Herbst Attorney-McGlew & Toren [57] ABSTRACT Hydraulically loaded rolling mills wherein the improvement comprises measuring means stretched over a distance between the measuring positions representing the roll gap of a rolling mill for measuring indirectly a change of the roll gup by detecting and signalling the tensile stress originated from elastic deformation of said measuring means.

8 Claims, 7 Drawing Figures PATENTEDJM 9197a 3. 709,007

sum 2 or 3 INVENTORS M umxo mm To s mHARu 'mrmsu BY mzuvosm HASH/H070 AKIRA H0203! WWW/M W7C ATTORNEYS m NAWW m R Hm m mu m m SH wmmA w w mkmfi PATENTEDJAH 9197s sum 3 or 3 HYDRAULICALLY LOADED ROLLING MILLS BACKGROUND OF THE INVENTION This invention relates to hydraulically loaded rolling mills including sensor responsive to tool-actuating fluid pressure. I

In prior art rolling practices, various means have been proposed for measuring roll gap in a hydraulically loaded rolling mills. A most typical one is the system as proposed for example in U.S. Pat. No. 3,398,559, U.S. Pat. No. 3,327,508 and Japanese Pat. application No. 44113/1965. The former two inventions, as apparent from their specifications, relate to a method and apparatus for controlling the operation having spacing means for setting the roll opening, said spacing means being mounted in the bearing chocks of one roll and bearing chocks of the other roll or between one of the roll assemblies and pre-stressing means.

The former two devices of the conventional technique both have spacing means of a very rigid construction and the load acted thereon is of a structure that is always subjected to the prestressing force which is larger than the separating force effected by the material-to-be-rolled present in the clearance between working rolls. Therefore, it needs a hydraulic cylinder larger in compressive force and it produces compressive plastic deformation from offset abutment of the spacer means against the back-up roll chocks. This results in that the accuracy of measurement and replaceability of parts are deteriorated so that complete maintenance is always necessitated. With respect to its construction, attachment surfaces for the adjust rod-load meters, i.e., the surfaces of the back-up roll chocks and the spacer means adapted to be respectively abutted againstthe upper and lower surfaces of the load meter, are adversely affected by vibration of the upper and lower roll chocks due to clearance between the roll chocks and the housing as is found quite inconvenient for maintaining their parallel rela tionship. Another difficulty is that, upon replacement of the back-up roll andconsequent replacement of the back-up roll chocks and spacing means, the spring constant and other characteristics of these members may not strictly conform to those before replacement so that errors would necessarily occur in the measurement. The invention'described in Japanese Pat. application No. 44113/1965 (Publication No. 1968/1967) has proposed a device for controlling a pressure adjuster means which comprises a displaceable adjust rod (weak spring) resiliently formed in a back-up roll chock for any one of opposed working rolls installed in a frame to carry an extremely small load as compared with the roll group respectively contacting the sides in the center of the roll, an adjust rod-load meter'for detecting the load acting on each adjust rod, and a roll load meter for detecting the load of the other roll out of the rolls in pair, wherein said pressure adjuster means exerts a hydraulic pressure on a hydraulic cylinder so that the ratio of output of said adjust rod-load meter to that of the roll load meter may be set in a value as predetermined.

In the technique disclosed in this invention, the displaceable adjust rod (spring) is formed resiliently to carry an extremely small load as compared with group so that it will certainly cause buckling. Even if it is not greatly subject to buckling, the adjust rod is bent forcibly into contact with the hole of the bearing chock, the resulting frictional resistance producing hysteresis loss and lowering of precision in the measurement. Such contact would easily occur when the bearing chock vibrates particularly during acceleration of the rolling mill, because of the clearance of the bearing chock and the frame. Further, at the instant when a load is applied on the adjust rod its natural frequency is lowered approximate to the responsive frequency of the control means and minor variation of the adjust rod-load meter due to vibration of the adjust-rod may sometimes exert undesired effect on the control means in the form of outer disturbance of the detector signal of the load meter. Then it is'required to have the adjust rod and adjust rod-load meter prevented from damage such as caused from striking great load at tail end of the rolled material. Therefore the adjust rod must be specially designed or a relatively large spring constant be used such that the rod can withstand the striking large load. However special construction of the adjust rod is inconvenient for manufacture and large spring constant of the adjust rod will require an excess compressive force to compress the adjust rod. Therein a hydraulic pressure cylinder of large compression force must be inevitably employed. At each occasion of replacement of the roll the bearing chock also must be changed so that a special care must be taken for preservation of parallel relationship of the adjust rod and the chock face, uniformity of characteristics, that is, replaceability thereof.

The inventors have studied the problem of these conventional systems from various viewpoints with the aim to overcome such disadvantages.

SUMMARY OF THE INVENTION This invention relates to an improved design for a hydraulically loaded rolling mill and more particularly said mill includes a novel roll gap measuring device.

It is an object of the invention to provide a novel, simplified and relatively inexpensive system.

It has been eventually found that the use of the spacer means or adjust rod not in the form of compression spring but as a tension spring is most adapted for the solution of the problem in order to detect the gap between the working rolls of the mill.

In accordance with the invention, a rolling mill comprising a pair of work rolls having bearing chock assemblies for rotatably supporting the work roll, or where necessary a pair of backup rolls for each work roll, having bearing chock assemblies for rotatably supporting the backup roll, hydraulically loaded means with at least a control valve adjusting the axial length of said means arranged at an adjoining or near place opposing to one of said work roll bearing chock assemblies or between said housing and one of said backup roll bearing chock assemblies for the adjustment of the gap between said work rolls, wherein the improvement comprises means stretched over a distance between the measuring positions representing the roll gap of a rolling mill for measuring indirectly a change of the roll gap by detecting and signalling the tensile force originated from elastic deformation of said measuring means, and a control system for adjusting said hydraulically loaded means in response to the signals of said measuring means to restore the amount of the roll gap to a predetermined one.

The function 'of the measuring means according to this invention will be easily understood when that of a spring balancer is considered. A spring balancer is intended to measure the weight of an object suspended by the spring from the elastic deformation of the spring. Contrary to this, the measuring and signalling means of the present invention is so designed that the force produced within the means is detected and the elastic deformation of the measuring means itself which has resulted in, such force in the measuring means is made known, whereby the change of the working roll gap can be indirectly measured. To cite the above-mentioned spring balancer for example, it is assumed that a tension type load cell is suspended fromv the hook of the spring balancer, the other end of the load cell being fixed (with the hook at the lower end of the load cell engaged with a fixed eyebolt, and the operator pulls up the upper end of the spring balancer with his both hands. In this case, the operator is unable to readthe graduation on the spring balancer in the pulled-up state. But if an ammeter connected to the load cell is attached to a point convenient for reading, the operator can easily find out the height up to which the upper end of thebalancer has been raised.

While the measuring means for the hydraulically loaded rolling mill according to this invention may be in' the form of a spring having relatively low spring force, it is preferable to set the allowable load so that, whenzthe measuring means is subjected to a tensile force which will causea given tensile power slightly greater than the upper measuring limit,.the proportional limit of themeans cannot be surpassed.

Further, in designing said measuring means, it is desirable to set the spring constant of the measuring means to a value not unreasonably high; the maximum tensile force which isproduced within the measuring means in its'range of measurement should not exceed thetotal of opening forces taking, into consideration the weight being borne by the members of the movable side of the mill in the. state whereno reaction force is applied between the working rolls, or, in a four high mill in which the members of the movable side are disposed below the .pass line as will be illustrated later with reference to the. accompanying drawings, the total of cylinders or yokes of the hydraulically loaded means connected tothe lower working roll mounted in the bearing chock assemblies and lower backup roll for said working roll, having bearing chock assemblies and measuring means, and the force with which the contact cylinder press said working roll against said backup roll.

If the tensile force of the measuring means in'the measuring range thereof comes equal to the total of the opening forces,.the movable side of the mill is suspended by the measuring means and, therefore, the

measuring means is not subjected to tensile force greaterithan the total opening forces regardless of the roll gap. The measuring means becomes unablev to indicate the exact roll gap and the initial gap between the working rolls cannot be set.

For the same reason, in a mill of the type wherein hydraulically loaded means and members of the movable side, are provided on the pass line, the tensile force of the measuring means must not be greater than the sum of the force of the balance cylinder which pushes up the bearing chock assemblies of the upper backup roll and the force of the balance. cylinder pressing the upper working roll against the upper backup roll minus the weights of the members of the movable side.

The foregoing limitations need not be taken into account, however, in designing the spring constant-for thin strip mills, foil mills and such other-mills wherein the upper and lower working rolls are kept in contact before the material to be rolled is passed therebetween.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments there of as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS I Three embodiments of the present invention are shown in the accompanying drawings, wherein FIG. 1 is a diagrammatic view explanatory of the first embodiment;

FIG. 2 is a fragmentary vertical-cross section showing an essential portion of FIG. 1;

FIG. 3 is a vertical section showing an essential portion of the second embodiment; I 1

FIG. 4 is a cross section taken along the line IV-IV of FIG. 3;

FIG. 5 is a diagrammatic view, partly in section, of a third embodiment;

FIG. 6 is a cross section taken along the line VIVI of FIG. 5 and FIG. 7 is a cross section takenalong the line VIIVII of FIG. 5, with a combined hydraulic control diagram.

DESCRIPTION OF THE EMBODIMENT The present invention will be described: more in detail by way of example on its one embodiments with reference to FIGS. 1 and 2. Numerals l and 2 denote work rolls having bearing chock assemblies. 3, 4 denote backup rolls which are supported in awindow frame of a housing 7 through backup roll chocks 5 and 6. Below the window frame is provided a hydraulic cylinder 8, by which the work rolls 2 are applied rolling load through the backup roll chock 6 and backup rolls 4. Numerals 10 and 10 designate measuring means, which are threadedly secured to the housing 7 by screw portions 9 at-each upper end of tension bars of, the measuring means so-as to be displaceable axially. Each lower end of the tension bars is connected to points at equal intervals from the roll center at the upper surface of said hydraulic cylinder 8. ll denotes a load cell for detecting the tension acting on the measuring means 10 and l0. l2 designates a position control means for the hydraulic cylinder 8 disposed in the circuit supplying oil pressure to the hydraulic cylinder 8; 13 a control means; and M a motor. A detailed construction of the measuring means 10, 10 is shown in FIG. 2. In the figure, the measuring means l0, 10 each consist of a tension bar 21, doughnut-shaped load cell 22, holding means 23, presser means 24, protection jacket 25, load limiter 26, connection means 27 and threaded portion 9, these being in assemblage as shown in FIG. 2 forming the measuring means 10. The tensile force of said measuring means I0, 10 must be less than the sum total'of the self weights of the hydrauliccylinder 8, lower backup roll 4, lower backup roll chocks 6, 6, lower work roll 2 with bearing chock assemblies, etc. and the pushing force of the contact cylinders (not shown) for pushing said work roll 2 against said back-up roll 4, under the condition that no reaction force is acting between the work rolls 1 and 2, but said tensile force must be large enough to remove the initial clearances at the threaded portion 9 and other portions and avoid influences due to disturbances. Thus it is necessary to set the spring constant of the measuring means 10 at such a value that the maximum tensile force produced in the measuring means 10, by elastic deformation may not cause substantial change to the work roll gap, at least, within the range of measurement. The piston 26a of the load limiter 26 is so constructed that it is compressed to its stroke end by a constant hydraulic pressure at all times. The holding means 23 and protection jacket 25 are connected with the connection means 27 having a slightly wider allowance than that of the range of measurement. Due to erroneous setting before rolling and abnormal load by pincher tree of strips, the tension bar 21 initially is elongated. Within the limit of resiliency of the bar 21 the holding means 23 and the protection jacket 25 cooperate to permit transmission of force through the connection means 27. Overcoming the pressing force of the load limiter 26 the piston 26a of the load limiter 26 is raised so as to protect the tension bar 21. The load limiter 26 may be a mechanical spring or a safety device such as a shear pin. At the lower part of the connection of the tension bar 21 with the protection jacket 25 there is provided a space 25a, which is intended to avoid excessive load probably occurring upon passing of the strip end during rolling between work rolls 1 and 2. The measuring means 10 of such construction as above described is mounted between the upper part of the housing 7 and the hydraulic cylinder 8 for detection of variation of the tensile force acting on the measuring means 10 and transmission of the force to the control means 13.

According to the invention, the measuring means 10 is employed as a detector for measurement of roll clearance, beside having the following functions and effects.

l. The tension bar 21 of the measuring means 10 may have a simple construction of a bar or plate shape, simple in sectional form,easy for manufacture, and capable of obtaining a detector of accurate spring constant.

2. The spring constant can be simply changed by control of length of the tension bar and the comparative correction of the detector can be facilitated.

3. The tension bar involves no hysteresis loss caused from friction with support means due to buckling or bending such as in compression spring. High accuracy detection can thus be obtained.

4. It is possible to use a pin for the attachment of the measuring means. Parallel load is provided in the load meter to elevate the accuracy of detection.

5. The tension bar 21 is used under tension load. Natural frequency of the measuring means 10 (detector) is therefore high. Even though the signal of vibration of the bar 21 shows disturbance it can be designed much higher than the responsive frequency of the control means so that it may not outer disturbance against the control system.

As may be apparent from the above-features, the tension spring type measuring system is excellent over the conventional compression spring type system in the overall detecting accuracy such as in the rolling mill which is large in rolling power and liable to be often disturbed at the measuring points-to-be-detected by disturbances of variation.

The second embodiment of the present invention shown in FIGS. 3 and 4 is an example of designing effective for shortening the overall length of the measuring means 10. As shown, the tension type load meter 31 is attached with a set of tension bars 32, 33 at ends through spring attachment 34. At the other ends are connected the lower ends of an intermediate fitting 35. A set of tension bars 36, 37 being tensioned between the upper part of said intermediate fitting 35 and the holder means 38. Otherwise, the invention provides the same construction as is shown in the above first embodiment. In this embodiment, the tension spring has a double construction by which it is shortened in overall length and made compact in the structure. It can obtain the effect of directly detecting the variation of tension of the tension springs 32, 33, 36 and 37 by the tension type load meter.

Another preferred embodiment of the hydraulically loaded rolling mill of the invention will be described hereunder with reference specifically to FIGS. 5, 6 and 7. FIG. 5, which is a side view of a rolling mill, shows only one half of the equipment and, actually, it is mated with the other half of the exactly same construction. FIG. 6 is a detailed view showing the construction of the upper part of a tension bar. In an actual mill each housing contains two sets of such tension bars but, for the simplicity of illustration, here is shown only one of the bars.

Referring first to FIG. 5, numeral 101 denotes a housing which rotatably supports an upper backup roll 52 and a lower backup roll 52' with bearing chocks 62, 62'. The housing also accommodates slidably upper and lower back-up roll assemblies 102, 102' consisting of working rolls 53, 53' and working roll chocks 63, 63, and upper and lower working roll assemblies 103, 103'. The inner wall of the housing is formed with grooves 10l'to hold the tension bars therein. In the lower part of the housing is provided a pushup cylinder 104 for hydraulic operation, which is associated with a 1 piston 105. Between the plunger 105 for the pushup cylinder and a sled 107 which is used for the changing of the backup rolls is interposed a tension bar connecting yoke 106, which is secured with bolts 131 to the plunger 105. Numeral 108 indicates a liner for adjusting the pass line. Connecting links 109 connect the tension bars and the plunger 105 for the push-up cylinder 105 through the yoke 1 06. Couplings 110 and 112 connect, respectively, the connecting links 109 and the lower parts of the tension bars 11 1, and the upper parts of the tension bars 111 and shafts 113. Although not shown, there are provided gaps between these connections to avoid subjection of the tension bars to any compressive force, in the same way as with the embodiment shown in FIG. 1. Casings for worm reduction gears to be used for position setting of the tension bars (i.e., for the setting of the roll positions) are indicated at 114. A screw 1 16 is used to adjust the height of pass line in case of any change due to replacement of the rolls. The screw is driven by a motor not shown via the worm reduction gears 115. Detailed description of its construction is omitted because the part is similar to those of the motor-driven mill currently in use. Nu-

the setting of each tension bar position is indicated at 118, one end of which being coupled to a motor not shown. A worm wheel 119 has a cylindrical inner space which is internally threaded as at 55 for thread engagement with a screw 120. A load cell 121 is mounted on the screw 120 through an upper spacer 122 and a lower spacer 122, and is used to detect the tensile force of the tension bar system. A liquid-pressure type load limiter 123 receives the upper end of the shaft 113 as a piston 56. .Guided by a guide rod 125, a spring 124 is secured in position'by a spring clamp plate 126 and a nut 127. In this embodiment the guide rod 125 is connected to '-the .piston 56 by screwing or other suitable method. The. spring 124 is intended to serve the following purpose. Whenthe lower backup roll assemblies 102' are to be replaced, the plunger 105 of the push-up cylinder 104 is brought down to the lower limit and the oil pressure of-the load limiter 123 is reduced. This would subject the tension bar lll'to its own weight and the combinedload of the connecting link 112 and the shaft 113 until the bar is bent. The spring 124 avoids this. In some cases the same effect'can be achieved" by either placing-the spring 124 underthe piston 56 inside the. load limiter 123 or suspending the piston from a tension spring.

Further, in accordance with the present invention, a safety device of hydraulic type herein called a load limiter 123 is provided to ensure the safety of the measuring means which is'- one of the most important components of a rolling mill and is a vital determinant for the mill performance. The operation and features of thedevice willbe described hereunder.

Under ordinary operating conditions, the shaft 113 is pressed against the upper stroke end of the load limiter 123 by a constant hydraulic pressure supplied to the limiter by a hydraulic pressure generating means not shown; Here let thepressing force or holdingforce (hereinafter called the holding force) which i is produced by the. constant hydraulic pressure supplied to the. load limiter 123 be R themaximum setting load ofthetension bars be Pb, and the safety strength of the tension bar system'including the load cell be T and if it is assumed that the three factors are so chosen as to hold a relationship Pb F T, then any excess tension which may be imposed on the tension bar system by any irregularity in the rolling operation, such as breakdownof the stripor drawing-in, or anyv excess tension caused by an erroneous maneuvering by the operator will beabsorbed by the load limiter 123.. Thus, safety is providedfor the tension bar system which is usedas the roll position measuring means, and safe and steady operation is. made possible. In short, the load limiter 123 avoids malfunction or damage of. the measuring means including the. tension bars 111 and the load cell 121 when the means are subjected to an overload fairly greater than its maximum setting load Pb A conventional safety device such as a shear pin or shear plate may serve the. safety purpose as well, but, once damaged, it will no longer be of use, whereas the load limiter 123 of hydraulic type can be reused in such case. Whenthe rolls are tobe replaced, the hydraulic pressure .:of theloadlimiter 123 can be released 'to lower the tension bars 111. This is advantageous because the screw on the upper part of each tension bar 111 maybe left intact.

Next, the construction and installation of the hydraulically loaded meansin the embodiment shown in FIG.

5 and the hydraulic control circuit therefor shown in FIG. '7 will be briefly explained. As shown, the push-up cylinder 104 is securely fastened to the lower end portion of the housing 101 with bolts 130. The yoke 106 is attached to the plunger 105 with bolts 131 as already described. The underside of the plunger 105 in the cylinder 104 is subjected to the action of high-pressure oil supplied from an oil pressure source 132 equipped with a hydraulic pump P to thelower oil feed port 133 of the cylinder 104 via a servo-valve S. V., and the upper side of the plunger 105 is subjected to the action of a low-pressure oil supplied from the same oil pressure source 132 but reduced in pressure by a reducing valve 134, so that the plunger 105 can be imparted with a pull-back force. Ordinary electric control amplifying means equipped with an electronic computer is generally indicated at 136..To the first input terminal 137 are given the control signals from the load cells 121, 121. Similarly, to the second input terminal 138 is given the signal based on the rolling pressure from the load .cell 117. The third input terminal 139 is supplied with standard setting signals, which are compared with values computed by. certain formulas from the'control signals and rolling pressure signals, and, depending on any errors thereby detected, control signals are supplied th'rough-the output terminal 140 to the servovalve S.V. The formulas for computation will not be explained here because they are the same as are used in conventional equipment of the character described.

Thus, because the yoke 106 and cylinder 104 are fixedly secured, respectively, to the. plunger 105 and housing 101 so that the plunger 105 may be subjected to a pull-back force, it is possible to control the pullback force and. the combined weight of the lower backup roll assemblies 102 and. other components as a force capable of counteracting the tensile force of the measuring means when the lower working roll assemblies 103' are being replaced and the weight of the assemblies 103' and the pushing force of the contact cylinder 65 has been removed.

It is also possible, where necessary, to set tension bars of a spring constant high enough to meet said pullback force and thus increase the mechanical strength of the measuring means. According to the above three embodiments, space position between the upper part of the housing and the hydraulically 'loaded means is measured as though it represents the roll clearance of the rolling mill. Such position of measurement is not limited to that which isxdescribed above.-It is apparent that the present invention also includes various different apparatuses such asithe apparatus for measuring at positions between the housing and the lower roll chock or between the hydraulic cylinder and the upper roll chock by measuring means orby utilizing the said ture, and maintenance, it greatly exceeds in overall detecting accuracy as compared with the conventional systems so as to obtain excellent industrial effects.

We claim:

1. A rolling mill comprising a housing, at least a pair of working rolls including bearing chock assemblies mounted within said housing, hydraulically loaded means mounted in said housing at one end thereof and having a movable member for applying rolling load to said working rolls, at least one servo valve for adjusting the axial length of said hydraulically loaded means, wherein the improvement comprises measuring means for measuring indirectly changes in the roll gap between said working rolls by detecting and signalling the tensile force originating from the elastic deformation of said measuring means, said measuring means operatively associated with said housing and said hydraulically loaded means and extending from the end of said housing in which said hydraulically loaded means are mounted to the opposite end of said housing and bridging the location within said housing of said working rolls, and a control system for adjusting said hydraulically loaded means in response to the signals from said measuring means for restoring the roll gap to a predetermined gap dimension.

2. A rolling mill, according to claim 1 wherein said measuring means includes at least one pair of tension bars extending from said hydraulically loaded means to the opposite end of said housing and having an allowable load which will not exceed the proportional limit with such tensile force which will cause at least a tensile strain to the upper measuring limit of said measuring means.

3. A rolling mill, according to claim 2, wherein said measuring means includes an intermediate fitting positioned between and spaced from said hydraulically loaded means and the opposite end of said housing with one of said tension bars extending between said hydraulically loaded means and said intermediate fitting and the other one of said tension bars extending between said intermediate fitting and the opposite end of said housing from said hydraulic loaded means.

4. A rolling mill, according to claim 2, wherein said hydraulically loaded means includes a yoke secured to said movable member thereof, and said measuring means includes two pair of said tension bars stretched between said housing and said yoke on said movable member of said hydraulically loaded means.

5. A rolling mill, according to claim 2, wherein said measuring means includes a hydraulically operated load limiter having a piston within a cylinder which piston in the normal condition is set on the stroke end of said cylinder but is moved to increase its normal length in an abnormal condition where said measuring means is subjected to an overload which exceeds the specified load and is greater than the tensile force which causes the tensile strain of the upper measuring limit but is less than the proportional limit of said tension bars of said measuring means.

6. A rolling mill, according to claim 2, wherein said measuring means includes mechanical protector means associated with said tension bars and having a clearance to avoid application of any compressive force on each said tensionbar in said measuring means,

specifically between the op osed ends of each said tension bar and the members 0 which said tension bar 15 connected.

7. A rolling mill, according to claim 2, wherein said measuring means comprises position setting means therefor, load cells for detecting the tensile stress of said measuring means and for generating a controlling signal, and a load limiter for avoiding overloading of said measuring means with said position setting means said load cells and said load limiter all mounted in the end of said housing opposite the end thereof containing said hydraulically loaded means.

8. A rolling mill, according to claim 2, wherein said hydraulically loaded means includes a cylinder fixedly secured to said housing, and a yoke connected to said measuring means and secured to said movable member of said hydraulically loaded means, and a hydraulic control device being combined with said cylinder and movable member to give a pull-back force to said hydraulically loaded means. 

1. A rolling mill comprising a housing, at least a pair of working rolls including bearing chock assemblies mounted within said housing, hydraulically loaded means mounted in said housing at one end thereof and having a movable member for applying rolling load to said working rolls, at least one servo valve for adjusting the axial length of said hydraulically loaded means, wherein the improvement comprises measuring means for measuring indirectly changes in the roll gap between said working rolls by detecting and signalling the tensile force originating from the elastic deformation of said measuring means, said measuring means operatively associated with said housing and said hydraulically loaded means and extending from the end of said housing in which said hydraulically loaded means are mounted to the opposite end of said housing and bridging the location within said housing of said working rolls, and a control system for adjusting said hydraulically loaded means in response to the signals from said measuring means for restoring the roll gap to a predetermined gap dimension.
 2. A rolling mill, according to claim 1, wherein said measuring means includes at least one pair of tension bars extending from said hydraulically loaded means to the opposite end of said housing and having an allowable load which will not exceed the proportional limit with such tensile force which will cause at least a tensile strain to the upper measuring limit of said measuring means.
 3. A rolling mill, according to claim 2, wherein said measuring means includes an intermediate fitting positioned between and spaced from said hydraulically loaded means and the opposite end of said housing with one of said tension bars extending between said hydraulically loaded means and said intermediate fitting and the other one of said tension bars extending between said intermediate fitting and the opposite end of said housing from said hydraulic loaded means.
 4. A rolling mill, according to claim 2, wherein said hydraulically loaded means includes a yoke secured to said movable member thereof, and said measuring means includes two pair of said tension bars stretched between said housing and said yoke on said movable member of said hydraulically loaded means.
 5. A rolling mill, according to claim 2, wherein said measuring means includes a hydraulically operated load limiter having a piston within a cylinder which piston in the normal condition is set on the stroke end of said cylinder but is moved to increase its normal length in an abnormal condition where said measuring means is subjected to an overload which exceeds the specified load and is greater than the tensile force which causes the tensile strain of the upper measuring limit but is less than the proportional limit of said tension bars of said measuring means.
 6. A rolling mill, according to claim 2, wherein said measuring means includes mechanical protector means associated with said tension bars and having a clearance to avoid application of any compressive force on each said tension bar in said measuring means, specifically between the opposed ends of each said tension bar and the members to which said tension bar is connected.
 7. A rolling mill, according to claim 2, wherein said measuring means comprises position setting means therefor, load cells for detecting the tensile stress of said measuring means and for generating a controlling signal, and a load limiter for avoiding overloading of said measuring means with said position setting means said load cells and said load Limiter all mounted in the end of said housing opposite the end thereof containing said hydraulically loaded means.
 8. A rolling mill, according to claim 2, wherein said hydraulically loaded means includes a cylinder fixedly secured to said housing, and a yoke connected to said measuring means and secured to said movable member of said hydraulically loaded means, and a hydraulic control device being combined with said cylinder and movable member to give a pull-back force to said hydraulically loaded means. 